My experiment is equivalent to two-interval, two-alternative forced choice. On each trial listeners hear two stimuli and judge the direction of the change between them, either "up" or "down". I believe that calculating d' in this experiment is just the same as for the standard 2I2AFC paradigm, which requires listeners to select an interval, 1st or 2nd.

Even though the probabilities of "up" and "down" trials are equal, I expect response biases (e.g., to respond "up" more than "down") and I want to calculate c for this. I'm wondering whether I should take the standard formula for c in YN (after redefining what is meant by a "hit" as responding up when the correct answer was up, and so on), then divide by sqrt(2).